Alkaline cell with improved cathode

ABSTRACT

An alkaline cell having an anode comprising zinc, an alkaline electrolyte solution, a separator, and a cathode comprising silver copper oxide selected from the compounds AgCuO 2  Ag 2 Cu 2 O 3  or any mixture thereof. The cathode preferably also includes a graphitic carbon to improve electrical conductivity. The graphitic carbon can comprise natural or synthetic graphites including expanded graphites and graphitic carbon fibers. The carbon nanofibers desirably have a mean average diameter less than 500 nanometers.

FIELD OF THE INVENTION

This invention relates to an aqueous alkaline cell with a cathode mixture comprising silver copper oxide AgCuO₂ or Ag₂Cu₂O₃ or mixtures thereof.

BACKGROUND OF THE INVENTION

Conventional alkaline electrochemical cells have an anode comprising zinc and a cathode comprising manganese dioxide. The cell is typically formed of a cylindrical casing. The casing is initially formed with an enlarged open end and opposing closed end. After the cell contents are supplied, an end cap with insulating plug is inserted into the open end. The cell is closed by crimping the casing edge over an edge of the insulating plug and radially compressing the casing around the insulating plug to provide a tight seal. A portion of the cell casing at the closed end forms the positive terminal.

Primary alkaline electrochemical cells typically include a zinc anode active material, an alkaline electrolyte, a manganese dioxide cathode active material, and an electrolyte permeable separator film, typically of cellulose or cellulosic and polyvinylalcohol fibers. The anode active material can include for example, zinc particles admixed with conventional gelling agents, such as sodium carboxymethyl cellulose or the sodium salt of an acrylic acid copolymer, and an electrolyte. The gelling agent serves to suspend the zinc particles and to maintain them in contact with one another. Typically, a conductive metal nail inserted into the anode active material serves as the anode current collector, which is electrically connected to the negative terminal end cap. The electrolyte can be an aqueous solution of an alkali metal hydroxide for example, potassium hydroxide, sodium hydroxide or lithium hydroxide. The cathode typically includes particulate manganese dioxide as the electrochemically active material admixed with an electrically conductive additive, typically graphite material, to enhance electrical conductivity. Optionally, polymeric binders, and other additives, such as titanium-containing compounds can be added to the cathode.

The manganese dioxide used in the cathode is preferably electrolytic manganese dioxide (EMD) which is made by direct electrolysis of a bath of manganese sulfate and sulfuric acid. The EMD is desirable since it has a high density and high purity. The resistivity of EMD is fairly low. An electrically conductive material is added to the cathode mixture to improve the electric conductivity between individual manganese dioxide particles. Such electrically conductive additive also improves electric conductivity between the manganese dioxide particles and the cell housing, which also serves as cathode current collector. Suitable electrically conductive additives can include, for example, conductive carbon powders, such as carbon blacks, including acetylene blacks, flaky crystalline natural graphite, flaky crystalline synthetic graphite, including expanded or exfoliated graphite. The resistivity of graphites such as flaky natural or expanded graphites can typically be between about 3×10⁻³ ohm-cm and 4×10⁻³ ohm-cm.

It is desirable for a primary alkaline battery to have a high discharge capacity (i.e., long service life). Since commercial cell sizes have been fixed, it is known that the useful service life of a cell can be enhanced by packing greater amounts of the electrode active materials into the cell. However, such approach has practical limitations such as, for example, if the electrode active material is packed too densely in the cell, the rates of electrochemical reactions during cell discharge can be reduced, in turn reducing service life. Other deleterious effects such as cell polarization can occur as well. Polarization limits the mobility of ions within both the electrolyte and the electrodes, which in turn degrades cell performance and service life. Although the amount of active material included in the cathode typically can be increased by decreasing the amount of non-electrochemically active materials such as polymeric binder or conductive additive, a sufficient quantity of conductive additive must be maintained to ensure an adequate level of bulk conductivity in the cathode. Thus, the total active cathode material is effectively limited by the amount of conductive additive required to provide an adequate level of conductivity.

It is desirable that the cell have high service life under normal drain rates, for example, between about 50 milliAmp and 500 milliAmp and also perform well in higher power application, at current rates between about 0.5 and 2.0 Amp, for example, between about 0.5 Amp and 1.5 Amp. Such high power application corresponds to a power output between about 0.5 and 1.5 Watt or even higher up to about 2.0 Watt. In conventional zinc/MnO₂ cells the utilization of anode/cathode active materials falls off as the current drain or power output requirements move into the high power regime.

Although such alkaline cells are in widespread commercial use there is a need to improve the cell or develop a new type of cell that exhibits reliable performance and longer service life for normal applications such as flashlight, radio, audio recorders and portable CD players and desirably also performs even better than conventional zinc/MnO₂ cells in high power applications.

SUMMARY OF THE INVENTION

The invention is directed to a primary (nonrechargeable) electrochemical alkaline cell having an anode comprising zinc and a cathode mixture comprising silver copper oxide selected from the compounds AgCuO₂ or Ag₂Cu₂O₃ or any mixture of AgCUO₂ and Ag₂Cu₂O₃. The term “silver copper oxide” as used herein, unless otherwise specified shall be understood to mean the compounds AgCuO₂, Ag₂Cu₂O₃ or mixtures thereof. The anode and cathode include an aqueous alkaline solution, preferably aqueous KOH solution. Such cell of the invention can be conveniently referenced herein as a Zn/Silver copper oxide alkaline cell. The silver copper oxide is preferably in the form of a powder having an average particle size between about 1 and 100 micron. The cathode mixture includes a conductive material such as flaky crystalline natural graphite or flaky crystalline synthetic graphite including expanded graphite and graphitic carbon nanofibers. The term graphitic carbon nanofibers as used herein shall mean graphitic carbon fibers having a mean average diameter less than 1000 nanometers (less than 1000×10⁻⁹ meter) (The term “average” or “mean average” as used herein shall mean the “arithmetic mean average” unless otherwise specified.) Preferably, the graphitic carbon nanofibers have a mean average diameter less than 500 nanometer, more preferably less than 300 nanometers. Desirably the graphitic carbon nanofibers have a mean average diameter between about 50 and 300 nanometers, typically between about 50 and 250 nanometers. The cathode mixture includes an aqueous KOH solution, desirably having a concentration of between about 30 and 40 percent by weight, preferably between 35 and 45 percent weight KOH in water.

It has been determined that in the Zn/Silver copper oxide alkaline cell of the invention the anode can comprise conventional gelled zinc anode compositions as in commercial use in conventional zinc/MnO₂ alkaline cells. By way of an example, not intended to be restrictive, the cathode can comprise the same composition as conventional cathode comprising MnO₂ as used in commercial zinc/MnO2 alkaline cells, except that the MnO₂ can be replaced in whole or in part by the AgCuO₂ or Ag₂Cu₂O₃ compounds, or any mixture of AgCuO₂ and Ag₂Cu₂O₃ compounds herein disclosed. The AgCuO₂ has been determined to have advantages when used as a cathode in alkaline cells. The copper in AgCuO₂ has a +3 valence and the silver a +1 valence. The Cu⁺³ and Ag⁺¹ are available for reduction to copper metal and silver metal during discharge. As a result the AgCuO₂ has a high theoretical specific capacity, namely, 526 milliAmp-hour/g. This is much higher than the theoretical specific capacity of MnO₂, which is 308 milliAmp-hour/g and higher than the theoretical specific capacity of AgO, which is 436 milliAmp-hour/g or Ag₂O, which is 117 milliAmp-hour/g. Additionally, the presence of silver (Ag⁺¹) and (Cu⁺³) in the AgCuO₂ compound causes an elevation in a Zn/AgCuO₂ alkaline cell's running voltage profile as compared to a Zn/MnO₂ or Zn/CuO alkaline cell. Ag₂Cu₂O₃ has copper at valence at +2 (Cu+2) which is lower than copper at valence +3 (Cu+3) in the AgCuO₂ compound, and therefore, has a theoretical specific capacity of 412 milliAmp-hour/g, which is lower than the specific capacity of 526 milliamp-hour/g for the AgCuO₂.

The Zn/Silver copper oxide alkaline cell exhibits a higher running voltage profile and longer service life than Zn/MnO₂ cells in normal applications, e.g. at drains rates between about 50 and 600 milliamp. It also exhibits a high rate capability for high power applications, for example, at current drains between about 0.5 and 1.5 Amp or power applications between about 0.5 and 1.5 Watt. For example, at a drain rate of about 1 Amp, between about 75 and 80 percent of the theoretical capacity of the AgCuO₂ can be utilized in a Zn/AgCuO₂ alkaline cell. The AgCuO₂, which has a copper valence of +3 (or Ag₂Cu₂O₃) is nevertheless sufficiently stable in water or aqueous KOH electrolyte solution. With respect to AgCuO₂, this compound does not react in water or aqueous KOH electrolyte during normal cell storage at room temperature as well as ambient temperatures between about −29° C. and 46° C. (−20° F. and 115° F.) to cause any significant degradation of the Cu+³ valence.

In a preferred embodiment, the silver copper oxide (AgCuO₂, or Ag₂Cu₂O₃ or mixtures thereof) comprises between about 82 and 90 percent by weight of the cathode mixture. In such embodiment the silver copper oxide can replace all of the manganese dioxide in the cathode. The performance of conventional Zn/MnO2 alkaline cells can also be improved if the silver copper oxide is used to replace a portion of the amount of MnO₂ conventionally used in the alkaline cell cathode. In such case the silver copper oxide can be mixed into the cathode with MnO₂. In either case, whether the AgCuO₂ is used alone or in admixture with MnO₂, the graphitic conductive material in the cathode, desirably comprises between about 2 and 10 percent by weight of the cathode, preferably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material desirably comprises expanded graphite or natural graphite alone or in any mixtures thereof. In such case the graphitic conductive material comprises between about 3 and 10 percent by weight of the cathode, desirably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material can contain only expanded graphite or only natural graphite or only graphitic carbon nanofibers, but can also contain natural graphite, expanded graphite and graphitic carbon nanofibers in any combination or mixture thereof. In such case the graphitic conductive material desirably comprises between about 4 and about 10 percent by weight of the cathode. The aqueous KOH solution desirably comprises between about 5 and 10 percent by weight of the cathode mixture. The aqueous KOH solution itself desirably comprises between about 30 and 40 percent by weight KOH, preferably between about 35 and 40 percent by weight KOH and about 2 percent by weight zinc oxide.

In one aspect the alkaline cell of the invention has an anode comprising-zinc and a cathode mixture comprising silver copper oxide in the form AgCuO₂. Such cell, for example, an AA size cell, exhibits high capacity (mAmp-hrs) and high energy output (mWatt-hours) under discharge rates between about 500 and 1000 mAmp when compared to same size conventional alkaline cell having an anode comprising zinc and cathode comprising manganese dioxide. This advantage would also apply to other size cylindrical cells, for example, AAAA, AAA, C and D size cells as well as AA cells.

In another aspect the alkaline cell of the invention has an anode comprising zinc and a cathode mixture comprising silver copper oxide in the form of Ag₂Cu₂O₃. Such cell, for example, an AA size cell, exhibits high capacity (mAmp-hrs) and high energy output (mWatt-hours) under discharge rates between about 500 and 1000 mAmp when compared to same size conventional alkaline cell having an anode comprising zinc and cathode comprising manganese dioxide. This advantage would also apply to other size cylindrical cells, for example, AAAA, AAA, C and D size cells as well as AA cells.

Although the embodiments herein are directed to a nonrechargeble cell, it may nevertheless be possible to produce a rechargeable cell with modified cathodes comprising AgCuO₂ designed to partially discharge to Ag₂Cu₂O₃, which in turn could be recharged back to AgCuO₂. Such cell, for example, could be an alkaline cell with a zinc anode discharging to zinc oxide, rechargeable back to zinc.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross sectional cut-away view of an elongated cylindrical alkaline cell having the cathode of the invention.

FIG. 2 is a cross sectional view of a cylindrical button alkaline cell having the cathode of the invention.

DETAILED DESCRIPTION

A representative alkaline cell utilizing the cathode mixture of the invention is shown in FIG. 1. The alkaline cell 810 comprises an elongated cylindrical casing 820 of steel, preferably nickel plated steel, having a closed end 814 and an open end 816. The cell is preferably filled with cathode mixture 812 of the invention comprising silver copper oxide (AgCuO₂, Ag₂Cu₂O₃ or mixtures thereof) which functions as cathode active material.

The copper in the compound AgCuO₂ has a +3 valence and the silver a +1 valence. The Cu⁺³ and Ag⁺¹ is available for reduction to copper metal and silver metal during cell discharge. As a result the AgCuO₂ has a high theoretical specific capacity, namely, 526 milliAmp-hour/g. (This is calculated as follows: 1 electron has the charge of 1.602×10⁻¹⁹ coulomb. Based on Avogadro's number there are 6.023×10²³ molecules per mole. 1 coulomb=1 Amp-sec. Assume theoretical reduction of the AgCuO₂ molecule during cell discharge on the basis of 4 electrons per molecule. Then, the theoretical capacity, milli-Amp per mol of AgCuO₂, is 4 electrons/molecule×6.023×10²³ molecules/mol×1.602×10⁻¹⁹ coulomb/electron=4×9.649×10⁴ coulomb/mol or 4×9.649×10⁴ Amp-sec/mol. The molecular weight of AgCuo₂ is 203.5. Thus, the theoretical capacity of AgCuO₂ is 4×9.649×10⁴ Amp-sec/mol×1 hour/3600 sec×1 mol/203.5 g=0.526 Amp/g=526 milliAmp/g. The compound Ag₂Cu₂O₃ has a lower theoretical specific capacity of about 412 mAmp-hr/g.

The cathode mixture 812 contains a conductive material, preferably a graphitic conductive material such as flaky crystalline natural graphite or flaky crystalline synthetic graphite, preferably expanded graphites or graphitic carbon nanofiber and mixtures thereof.

The term “graphite” or “graphitic material” as used herein shall include natural and synthetic crystalline graphites, expanded graphites, graphitic carbons, and graphitic carbon fibers. A graphitic carbon has the characteristics of an ordered three-dimensional graphite crystalline structure consisting of layers of hexagonally arranged carbon atoms stacked parallel to each other as determined by X-ray diffraction. As defined in International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the Journal Carbon, Vol. 20, p. 445 a graphitic carbon embraces the varieties of substances consisting of elemental carbon in allotropic form of graphite irrespective of of structural defects. The term graphitic carbon as used herein shall be construed in this manner.

The term carbon fibers shall mean elongated strands of carbon having length to diameter ratio greater than 4, typically greater than 8. The length to diameter ratio of carbon fibers can be much higher, for example, greater than 100 or more. The term “natural crystalline graphite” as used herein shall mean graphite that is minimally processed, i.e., essentially in its geologically occurring natural crystalline form. The term “synthetic graphite” as used herein shall mean synthetically prepared or processed graphite. The term “synthetic graphite” as used herein unless further qualified is also intended to include expanded forms of graphite (including expanded graphite that has been exfoliated) and graphitic carbon nanofibers. The term “expanded graphite” is a recognized term of art, for example, the form of graphite generally as referenced in U.S. Pat. No. 5,482,798. Further, expanded graphite as used herein can be formed from natural and/or synthetic non-expanded graphite processed so as to have a uniaxially expanded crystal lattice. The extent of uniaxial expansion can be sufficiently large such that the expanded graphite particles can completely exfoliate (i.e., separate into thin laminae). The term “flaky” as commonly used in connection with graphites, (i.e., natural or synthetic flaky graphites) is intended to reflect that such graphites have a plate-like, non-expanded particle form.

The graphitic conductive material is added to the AgCuO₂ active material to form the cathode of the invention. The graphitic conductive material desirably comprises between about 2 and 10 percent by weight of the cathode mixture, preferably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material desirably comprises expanded graphite or natural graphite alone or in any mixtures thereof. In such case the graphitic conductive material comprises between about 3 and 10 percent by weight of the cathode, desirably between about 4 and 10 percent by weight of the cathode. The graphitic conductive material can contain only expanded graphite or only natural graphite or only graphitic carbon nanofibers, but can also contain natural graphite, expanded graphite and graphitic carbon nanofibers in any combination or mixture thereof. In such case the graphitic conductive material desirably comprises between about 4 and about 10 percent by weight of the cathode. The aqueous KOH solution desirably comprises between about 5 and 10 percent by weight of the cathode mixture. It has been determined that expanded graphite provides a desirable graphitic conductive material when used alone or in admixture with natural graphite to be added to the AgCuO₂ cathode active material. However, the graphitic carbon nanofibers can also be added to form a portion of the graphitic conductive material as above mentioned. Such graphitic carbon nanofibers, per se, are referenced in the published art and specific methods of manufacture are disclosed, for example, in U.S. Pat. Nos. 5,594,060; 5,846,509 and 6,156,256.

The term graphitic carbon fibers as used herein shall mean carbon fibers having a graphitic carbon structure as defined by the International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the Journal Carbon, Vol. 20, p. 445. The graphitic carbon nanofibers as used herein shall mean graphitic carbon fibers having a mean average diameter less than 1000 nanometers (less than 1000×10⁻⁹ meters). (The term “average” or “mean average” as used herein, unless otherwise specified, shall be understood to mean the arithmetic mean average.) Preferably, the graphitic carbon nanofibers have a mean average diameter less than 500 nanometer, more preferably less than 300 nanometers. Desirably the graphitic carbon nanofibers have a mean average diameter between about 50 and 300 nanometers, typically between about 50 and 250 nanometers. The graphitic carbon nanofiber useful in the cathode mixture 812 of the invention has a mean average diameter desirably less than about 300 nanometers, preferably between about 50 and 250 nanometers, typically about 200 nanometers. The mean average length of the carbon nanofibers is desirably between about 0.5 and 300 micron, typically about 200 micron. The graphitic carbon nanofibers can have a BET surface area between about 15 and 50 m²/g, typically between 15 and 30 m²/g. Such graphitic carbon nanofibers can be in the form of individual fiber strands including agglomerates of such fiber strands. A preferred graphitic carbon nanofiber for use in the cathode mixture 812 of the invention is a vapor grown graphitic carbon fiber available under the trade designation PR19HT carbon fibers from Applied Sciences, Cedarville, Ohio. Such graphitic carbon nanofibers can be made by hydrocarbon vapor pyrolysis methods described, for example, in Applied Sciences U.S. Pat. Nos. 6,156,256; 5,846,509; and 5,594,060 herein incorporated by reference. The resulting carbon nanofibers have a graphitic carbon structure as defined in International Committee for Characterization and Terminology of Carbon (ICCTC, 1982), published in the Journal Carbon, Vol. 20, p. 445. The vapor grown carbon fibers described in the above patent references are graphitic carbon fibers which can be made by the pyrolysis of hydrocarbon, for example, methane in a gas phase reaction at temperatures of around 1000° C. or higher. The gas phase reaction involving the hydrocarbon is carried out upon contact with metal particles, typically iron particles in a nonoxidizing gas stream. The iron particles catalyze the growth of very thin individual carbon fibers (e.g. carbon nanofibers) which have a graphitic carbon structure. The resulting carbon fibers can have a very thin diameter (nanofibers), for example, between 50 and 300 nanometers such as that available under the trade designation PR19HT graphitic carbon nanofibers (Applied Sciences).

It has been determined that the iron (or other metal) impurity which are residual catalyst impurities imbedded in the graphitic carbon nanofiber can be readily removed therefrom by subjecting the nanofibers to heating at temperatures between about 2500° C. and 3100° C. after the fibers have been formed. Such heating vaporizes the metal impurities and can also serve to further graphitize the carbon fiber, particularly the surface of the fibers. The end result is a purified graphitic carbon nanofiber desirably contains less than 200 ppm, preferably less than 100 ppm, more preferably less than 50 ppm metal. (The term metal shall include all metal whether in elemental, ionic or chemically bound in compounds.) Such graphitic carbon nanofiber can form a portion of the graphitic carbon material to be added to the AgCuO₂ cathode active material. For example, such graphitic carbon nanofiber can be admixed with natural graphite or expanded graphite as above mentioned.

The cathode mixture 812 comprising AgCuO2 includes an aqueous KOH electrolyte solution and the mixture can be prepared wet, with aqueous KOH included before the mixture is inserted into the cell. For example, the casing 820 can be filled with the cathode mixture and the central portion of the cathode mixture can be excavated leaving the annular cathode 812 as shown in FIG. 1. The wet cathode mixture can be compacted while in the cell. Alternatively, the wet mixture can be compacted into disks 812 a before insertion into the cell and then, optionally, additionally compacted while in the cell. Alternatively, the cathode mixture 812 can be prepared by first dry mixing the silver copper oxide, and graphite material optionally added. The dry mixture can be compacted into the cell casing 820 or can be compacted into disk shaped blocks 812 a, which can be inserted into the cell in stacked arrangement. A separator sheet 890 can be placed against the inside surface of cathode disks 812 a. Separator 890 can be of cellulosic film or a film formed of nonwoven material comprising polyvinylalcohol and rayon fibers. Separator 890 can be of a single layer of such nonwoven material or can be a composite having layer of cellophane adhered to the nonwoven material. The nonwoven material can typically contain polyvinylalcohol fibers and rayon fibers. Separator 890 can be positioned so that the cellophane layer is adjacent to either cathode 812 or anode 815. Separators conventionally used in zinc/silver oxide alkaline cells can be used advantageously for separator 890 in the present cell 810 having a cathode 812 comprising silver copper oxide. Separator 890 can be prepared from a radiation graft of methacrylic acid onto a polyethylene membrane. Separator 890 in such form retards the migration of copper and silver ions to the anode compartment. AgCuO₂ has a slight solubility (e.g. less than about 1 weight percent) in aqueous potassium hydroxide. Thus, a small amount of the silver and copper ions from AgCuO₂ are present in solution within the aqueous potassium hydroxide electrolyte present in the cathode mixture 815. The grafted separator is particularly desirable since it tends to retard migration of silver and copper ions from the cathode to the anode. Aqueous KOH electrolyte can be poured over the dry cathode wherein it becomes absorbed into the separator and cathode. The anode material 815 can then be added to the cell.

The silver copper oxide (AgCuO₂) can be prepared by the reaction between a silver nitrate (AgNO₃) and copper nitrate, (CuNO₃) utilizing an oxidizing solution of KOH and K₂S₂O₈ with the reaction carried out at about 90° C. temperature. A method of synthesis according to the above reaction is described in J. Curda, W. Klein, and M. Jansen, “AgCuO₂ Synthesis, Crystal Structure, . . . ”, Journal of Solid State Chemistry, Vol. 162, pp. 220-224 (2001). Specifically, as stated in the above reference, microcrystalline AgCuO₂ can be synthesized by reacting saturated aqueous solution of 1.205 g (5 mMol) of AgNO₃ (Merck, 99%) and 0.85 g (5 mMol) of Cu(NO₃)₂H₂O by adding a solution of 3.0 g of KOH and 1.5 g of K₂S₂O₈ in 150 ml of water at 90° C. The microcrystalline AgCuO₂ forms as a precipitate. The unique microcystalline structure of the AgCuO₂ is illustrated in FIG. 6 of the above reference. The AgCuO₂ precipitate is filtered off, washed with deionized water and dried in air at 70° C. Another means of forming AgCuO₂ (alluded to in the above reference) is by oxidation of an aqueous suspension of Ag₂Cu₂O₃ as reported in the reference K. Adelsberger, J. Curda, S. Vensky, and M. Jansen, J. Solid State Chem., Vol. 158, p. 82 (2001). A method of preparing Ag₂Cu₂O₃ is given in K. Adelsberger et. al., supra, J. Solid State Chem., Vol. 158, at p. 82, as follows: “Black crystals of Ag₂Cu₂O₃ can be prepared by solid state reaction of Ag₂O (precipitated from an acidic AgNO₃ solution) and CuO (Aldrich, 99%) in a high oxygen pressure. The binary oxides can be mixed in a 1:1 molar ratio and then annealed for 3-5 days in silver crucibles placed in stainless steel autoclaves. The optimized reaction temperature and oxygen pressure are 500° C. and 200 Mpa, respectively. One milliliter of a 7 M KOH aqueous solution is added as an accelerator. Microcrystalline, black powder of Ag₂Cu₂O₃ is precipitated from an aqueous solution of AgNO₃ (Merck, p.a., 99.5%) and CuNO₃.3H₂O (Panreac, p.a., 99.98%) adding 4 ml NaOH solution (3M). The precipitate is dried in air at 90° C. for 24 hours.”

The silver copper oxide prepared by the above methods can be used in cathode mixture 812. The silver copper oxide for use in cathode 812 is a powder having an average particle size (dry) between about 1 and 100 micron. The silver copper oxide, AgCuO₂, has a real density of about 7.1 g/cc and a BET surface area of about 10-100 m²/g, for particles sizes between about 1 and 100 micron. The Ag₂Cu₂O₃ has a real density of about 7.0 g/cc. The real density of a solid is the weight of the sample divided by the real volume. The real volume of a sample is the actual volume less volume occupied by entrapped air between the particles and pores within the particles. The BET surface area (m²/g) (Brunauer, Emmett and Taylor method) is the standard measurement of particulate surface area by gas (nitrogen and/or other gasses) porosimetry as is recognized in the art. The BET surface area measures the total surface area on the exterior surface of the particle and also that portion of surface area defined by the open pores within the particle available for gas adsorption and deadsorption when applied.

Anode 815 comprises zinc and aqueous KOH electrolyte. The electrolyte in the anode comprises a conventional mixture of KOH, ZnO and gelling agent. The zinc serves as the anode active material. The anode and cathode can be separated by a conventional ion porous separator 890, for example, comprising polyvinylalcohol and cellulosic fibrous material. After cell 810 is filled an insulating plug 860 is inserted into open end 816. Insulating plug 860 may be of polypropylene, talc filled polypropylene, sulfonated polyethylene or nylon. Plug 860 can have a thinned portion 865 therein typically of a small circular, oval or polygonal shape. Thinned portion 865 functions as a rupturable membrane which can be designed to rupture thereby releasing excessive gas within the cell. This guards against excessive buildup of gas pressure within the cell, for example, if the cell is subjected to excessive heat or abusive operating conditions. The plug 860 is preferably snap fitted around circumferential step 818 as shown in the figure so that the plug locks in place into the open end 816. The peripheral edge 827 of casing 820 is crimped over the top of insulating plug 860. A paper insulating washer 880 is applied over the crimped peripheral edge 827 of casing 820. Insulating washer 880 can be a polyethylene coated paper washer. A terminal end cap 830 is welded to the head of current collector 840. An elongated current collector 840 is then inserted (force fitted) into aperture 844 of insulating plug 860 so that end cap 830 comes to rest against insulating washer 880. Current collector 840 can be selected from a variety of known electrically conductive metals found to be useful as current collector materials, for example, brass, tin plated brass, bronze, copper or indium plated brass. The current collector 840 used in the test cells was of brass. Conventional asphalt sealant may be preapplied around the current collector 840 before it is inserted into aperture 844. A film label 870 is applied around casing 820. The terminal end cap 830 becomes the negative terminal of alkaline cell 810 and pip 825 at the closed end of casing 820 becomes the positive terminal.

The cell 810 shown in FIG. 1 can be an AA cell. However, the alkaline cell shown in the figure is not intended to be restricted to any particular size. Thus, the present invention is applicable to AAAA, AAA, C and D size cylindrical alkaline cells as well as button size or prismatic alkaline cells of any size or shape. Alkaline cell 810 is not intended to be restricted to any particular cell chemistry or cell size, except that the cathode 812 is prepared utilizing the cathode mixture of invention comprising silver copper oxide and graphite material. The above cell (FIG. 1) can be an AAAA, AAA, AA, C or D cells. These standard cell sizes are recognized in the art and are set by the American National standards Association or in Europe by the International Electrotechnical Commission (IEC). The AA cylindrical cell as referenced herein had standard overall dimensions as given by the American National Standards Institute (ANSI) battery specification ANSI C18.1M, Part 1-1999 as follows: The overall length from positive and negative terminal tips is between 49.2 mm and 50.5 mm and overall outside cell diameter is between 13.5 mm and 14.5 mm.

Thus cell 810 can contain conventional alkaline cell zinc anode chemistries including those which contain zero added mercury (less than 50 parts mercury per million parts total cell weight, preferably less than 10 parts mercury per million parts total cell weight) and modifications thereof. Such representative chemistries, for example, are disclosed in U.S. Pat. No. 5,401,590, herein incorporated by reference. The cell 810 of the invention also preferably does not contain added amounts of lead and thus can be essentially lead free, that is, the total lead content is less than 30 ppm, desirably less than 15 ppm of total metal content of the anode.

An alkaline cell having a gelled zinc anode and the cathode of the invention comprising silver copper oxide cathode active material (AgCuO₂, Ag₂Cu₂O₃ or mixtures thereof) can also be fabricated in the form of a button or coin cell 110 as shown in FIG. 2. The cell 110 can include a cathode 170 comprising the cathode mixture of the invention. Such cathode mixtures, can comprise silver copper oxide, 82 to 90 wt. %, graphite, for example, expanded graphite, between about 4 and 10 wt. %, and between about 5 and 10 wt. % of aqueous KOH electrolyte (aqueous KOH electrolyte is 30 to 40 wt. % KOH concentration, preferably between 35 and 40 wt. % KOH concentration). The aqueous KOH electrolyte preferably also contains about 2 wt. % ZnO. The cathode mixture can optionally also comprise between about 0.1 to 0.5 wt % of a polyethylene binder.

The anode material 150 comprises: Zinc alloy powder 62 to 69 wt % (99.9 wt % zinc containing indium), an aqueous KOH solution comprising 38 wt % KOH and about 2 wt % ZnO; a cross-linked acrylic acid polymer gelling agent available commercially under the tradename “CARBOPOL C940” from B. F. Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrile grafted onto a starch backbone commercially available commercially under the tradename “Waterlock A-221” from Grain Processing Co. (between 0.01 and 0.5 wt. %); dionyl phenol phosphate ester surfactant available commercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm). The zinc alloy average particle size is desirably between about 30 and 350 micron. The bulk density of the zinc in the anode (anode porosity) is between about 1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent by volume of the aqueous electrolyte solution in the anode is between about 69.2 and 75.5 percent by volume of the anode. It shall be understood that the term zinc as used herein shall include such zinc alloy powder, since the alloy powder is composed almost entirely of zinc and functions electrochemically as zinc.

The separator 160 can be a conventional ion porous separator as described above with respect to separator 890. In the specific embodiment shown in FIG. 2, referenced in the examples, the separator 160 comprises an outer layer of cellulose and an inner layer of a nonwoven material composed of cellulosic (rayon) and polyvinylalcohol fibers. The outer layer of cellulose abutted the cathode electrode.

In the button cell 110 shown in FIG. 2, a disk-shaped cylindrical housing 130 is formed having an open end 132 and a closed end 38. Housing 130 is formed from nickel-plated steel. An electrical insulating member 140, preferably a cylindrical member having a hollow core, is inserted into housing 130 so that the outside surface of insulating member 140 abuts and lines the inside surface of housing 130. Alternatively, the inside surface of housing 130 can be coated with a polymeric material that solidifies into insulator 140 abutting the inside surface housing 130. Insulator 140 can be formed from a variety of thermally stable insulating materials, for example, nylon or polypropylene.

The cathode mixture 170 comprising silver copper oxide (AgCuO₂), graphite, aqueous electrolyte can be prepared by simple mixing at ambient temperature in a conventional blender until a homogenous mixture is obtained. The graphite can be flaky natural crystalline graphite, flaky crystalline synthetic graphite, expanded graphite or any mixture thereof. The cathode 170 is applied as a layer or a pressed disk abutting the inside surface of the closed end 138 of housing 130. The separator sheet 160 is placed overlying cathode 170. Additional aqueous electrolyte can be added so that electrolyte fully penetrates through separator sheet 160 and cathode 170. A layer of anode mixture 150 comprising particulate zinc, aqueous KOH electrolyte solution (35-40 wt % KOH and 2 wt. % ZnO), and gelling agent is applied to the separator sheet 160. The anode cover 120, formed preferably of nickel-plated steel, is inserted into the open end 132 of housing 130. An anode current collector 115 comprising a sheet of brass, tin-plated brass, bronze, copper or indium-plated brass can optionally be welded to the inside surface of anode cover 120. Peripheral edge 135 of housing 130 is crimped over the exposed insulator edge 142 of insulating member 140. The peripheral edge 135 bites into insulator edge 142 closing housing 130 and tightly sealing the cell contents therein. The anode cover 120 also functions as the negative terminal of the cell and the housing 130 at the closed end 138 functions as the cell's positive terminal.

Test cylindrical button cells 110 can be prepared, for example, having a diameter of 15.0 mm and depth of 6.98 mm.

In test button cells 110 the separator 160 can be a conventional ion porous separator consisting of an inner layer of a nonwoven material of cellulosic (rayon) and polyvinylalcohol fibers and an outer layer of cellophane. The same anode mixture comprising particulate zinc can be used in each test cell. The cathode composition can be varied. The performance of the cells, service life (milliamp-hrs) and energy output (milliwatt-hrs) can be determined by discharging at a given current, milliAmp or current density milliAmp/cm2 (current density at anode/cathode interface) to a specific cut off voltage, for example of 0.9 Volts.

In the tests reported in the following examples the test cells were AA cylindrical cells 810 of the type shown in FIG. 1. In the case of the comparative test (Example 1) using an anode comprising zinc and a cathode comprising MnO₂, the AA size cells 810 were balanced on the basis that milliamp-hrs capacity of zinc (based on 810 milliamp-hours per gram zinc) divided by the milliamp-hrs capacity of MnO₂ (based on 308 milliamp-hours per gram MnO₂) is about 1. In the cells tested (Examples 2) using an anode comprising zinc and cathode comprising silver copper oxide (AgCuO₂) or (Ag2Cu2O3). The AA size cells 810 were balanced on the basis that the milliamp-hrs capacity of zinc (based on 810 milliamp-hours per gram zinc) divided by the milliamp-hrs capacity of silver copper oxide and MnO₂ in the cathode mixture (based on 526 milliamp-hours per gram AgCuO₂, 412 milliAmp-hrs per gram Ag₂Cu₂O₃, and 308 milliamp-hrs per gram MnO₂) is in slight excess of 1.

EXAMPLE 1 (Comparative—Zinc Anode; MnO2 Cathode)

Test cylindrical AA cells of the general configuration shown in 810 (FIG. 1) were prepared. Test cells 810 were prepared with a anode 815 comprising Zinc alloy powder 62 to 69 wt % (99.9 wt % zinc containing indium), an aqueous KOH solution comprising 38 wt % KOH and about 2 wt % ZnO; a cross-linked acrylic acid polymer gelling agent available commercially under the trade name “CARBOPOL C940” from B. F. Goodrich (e.g., 0.5 to 2 wt %) and a hydrolyzed polyacrylonitrile grafted onto a starch backbone commercially available commercially under the tradename “Waterlock A-221” from Grain Processing Co. (between 0.01 and 0.5 wt. %); dionyl phenol phosphate ester surfactant available commercially under the tradename “RM-510” from Rhone-Poulenc (50 ppm). The zinc alloy average particle size is desirably between about 30 and 350 micron. The bulk density of the zinc in the anode is between about 1.75 and 2.2 grams zinc per cubic centimeter of anode. The percent by volume of the aqueous electrolyte solution in the anode is between about 69.2 and 75.5 percent by volume of the anode. The separator 890 was a conventional dual layered cellulosic separator employing an outer layer comprising rayon and polyvinylalcohol (facing cathode 812) and inner layer of cellophane facing anode 815.

The cathode 812 has the following representative composition: 80-87 wt % of electrolytic manganese dioxide (e.g., Trona D from Kerr-McGee), 4-10 wt % of expanded graphite (Timcal E-BNB90, BET surface of 24.3 m²/g ), 5-10 wt % of an aqueous KOH solution having a KOH concentration of about 35-40 wt. %. The cathode 812 had 9.59 grams of MnO₂ and was balanced with an amount of zinc in anode 815 calculated as above described so that the theoretical capacity of the zinc divided by the theoretical capacity of the MnO₂ was about 1. A specific cathode composition which was used for Example 1 is as follows:

Cathode Composition¹ Wt. % MnO₂ (EMD) 87 Expanded graphite 7 (Timcal E-BNB90) KOH aqueous 6 Solution (36 wt % KOH and 2 wt % ZnO) 100 Notes: 1. Conversion to volume percent can be made using the following real densities: MnO₂ (EMD), 4.48 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

The AA cells 810 of Example 1 were discharged at a constant rate of 250 milliAmp (current density of about 21 milliAmp/cm²) to a cut off voltage of 0.9 volts. In separate tests batches of fresh AA cells 810 of Example 1 were discharged at a constant rate of 1 Amp.

At discharge of 250 milliAmp, the capacity obtained at a cut off voltage of 0.9 Volts was 2227 milliAmp-hrs. The specific capacity of the MnO₂ was 232 milliAmp-hours per gram. The energy output of the cell was 2004 milliwatt-hrs.

At discharge of 1 Amp, the capacity obtained at a cut off voltage of 0.9 Volts was 917 milliAmp-hrs. The specific capacity of the MnO₂ was 95.5 milliAmp-hours per gram. The energy output of the cell was 825 milliwatt-hrs.

EXAMPLE 2

Test AA size cells 810 were prepared as in Example 1 except that the cathode 812 is formed of the following cathode mixture of the invention comprising silver copper oxide (AgCuO₂). The anode composition comprising gelled zinc was the same as used in Example 1. The cell has 10.3 grams AgCuO₂ and was balanced so that the theoretical capacity of the zinc divided by the theoretical capacity of the AgCuO₂ was about 1. The same composition of cathode was used except that the MnO₂ was replaced with AgCuO2. Graphite material in the form of expanded graphite was added.

Cathode Composition¹ Wt. % AgCuO₂ 87 Expanded graphite 7 (Timcal E-BNB90) KOH aqueous 6 Solution (36 wt % KOH and 2 wt. % ZnO) 100 Notes: 1. Conversion to volume percent values can be made using the following real densities: AgCuO₂, 7.1 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

The AA cells 810 of Example 2 were discharged at a constant rate of 250 milliAmp (current density of about 21 milliAmp/cm²) to a cut off voltage of 0.9 volts. In separate tests batches of fresh AA cell of Example 2 were discharged at a constant rate of 1 Amp.

At discharge of 250 milliAmp, the capacity obtained at a cut off voltage of 0.9 Volts was 2947 milliAmp-hrs. The specific capacity of the AgCuO₂ was 287 milliAmp-hours per gram. The energy output of the cell was 2652 milliwatt-hrs.

At discharge of 1 Amp, the capacity obtained at a cut off voltage of 0.9 Volts was 2210 milliAmp-hrs. The specific capacity of the AgCuO₂ was 207 milliAmp-hours per gram. The energy output of the cell was 1989 milliwatt-hrs.

EXAMPLE 3

Test AA size cells 810 were prepared as in Example 1 except that the cathode 812 is formed of the following cathode mixture of the invention comprising silver copper oxide (Ag₂Cu₂O₃). The anode composition comprising gelled zinc was the same as used in Example 1. The cell had 9.86 grams of Ag₂Cu₂O₃ and was balanced so that the theoretical capacity of the zinc divided by the theoretical capacity of the AgCuO₂ was in slight excess of 1. The same composition of cathode was used except that the MnO2 was replaced with Ag₂Cu₂O₃. Graphite material in the form of expanded graphite was added.

Cathode Composition¹ Wt. % Ag₂Cu₂O₃ 87 Expanded graphite 7 (Timcal E-BNB90) KOH aqueous 6 Solution (36 wt % KOH and 2 wt. % ZnO) 100 Notes: 1. Conversion to volume percent values can be made using the following real densities: Ag₂Cu₂O₃, 7.0 g/cc; expanded graphite (Timcal E-BNB90), 2.25 g/cc; and 36 wt % KOH aqueous solution, 1.35 g/cc.

The AA cells 810 of Example 2 were discharged at a constant rate of 250 milliAmp (current density of about 21 milliAmp/cm²) to a cut off voltage of 0.9 volts. In separate tests batches of fresh AA cell of Example 3 were discharged at a constant rate of 1 Amp.

At discharge of 250 milliAmp, the capacity obtained at a cut off voltage of 0.9 Volts was 2247 milliAmp-hrs. The specific capacity of the AgCuO₂ was 228 milliAmp-hours per gram. The energy output of the cell was 2584 milliwatt-hrs.

At discharge of 1 Amp, the capacity obtained at a cut off voltage of 0.9 Volts was 1143 milliAmp-hrs. The specific capacity of the AgCuO₂ was 116 milliAmp-hours per gram. The energy output of the cell was 1315 milliwatt-hrs.

The performance results of the examples are summarized in Table 1 for discharge at 250 milliAmp and Table 2 for discharge at 1 Amp.

TABLE 1 AA Alkaline Cell With Zinc Anode and Cathode Comprising AgCuO₂ Discharged at 250 milliAmp to 0.9 V Specific Capacity Cathode Active Material Capacity, (MnO₂ or mAmp- Energy Out, AgCuO₂) Example Cathode hrs mWatt-hrs mAmp-hrs/g 1 Com- MnO₂ (EMD) and 2227 2004 232 parison Expanded Graphite 2 AgCuO₂ and 2947 2652 287 Expanded Graphite 3 Ag₂Cu₂O₃ and 2247 2584 228 Expanded Graphite

TABLE 2 AA Alkaline Cell With Zinc Anode and Cathode Comprising AgCuO2 Discharged at 1 Amp to 0.9 V Specific Capacity Cathode Active Material Capacity, (MnO₂ or mAmp- Energy Out, AgCuO₂) Example Cathode hrs mWatt-hrs mAmp-hrs/g 1 Com- MnO₂ (EMD) and 917 825 95.5 parison Expanded Graphite 2 AgCuO₂ and 2210 1989 207 Expanded Graphite 3 Ag₂Cu₂O₃ and 1143 1315 116 Expanded Graphite

As shown in Table 1 the alkaline cells of the invention with silver copper oxide cathode active material (Examples 2) discharged at 250 milliAmp exhibits a higher capacity and higher power output than the same size conventional Zn/MnO₂ alkaline cell discharged at same rate. The increase in capacity and power output of the alkaline cell of the invention with silver copper oxide cathode is more pronounced at higher discharge rate of 1 Amp as shown in Table 2.

Although the invention has been described with respect to specific embodiments, it will be appreciated that variations are possible within the concept of the invention. Thus, the invention is not intended to be limited to the specific embodiments herein described, but is better defined by the claims and equivalents thereof. 

What is claimed is:
 1. An electrochemical cell comprising a housing, a positive and a negative terminal, an anode comprising an anode active material, an aqueous alkaline electrolyte solution, a separator, and a cathode comprising a cathode active material selected from the group of compounds consisting of AgCuO₂, Ag₂Cu₂O₃ and mixtures thereof.
 2. The cell of claim 1 wherein said cell is nonrechargeable.
 3. The cell of claim 1 wherein the anode active material comprises zinc.
 4. The cell of claim 1 wherein the electrolyte solution comprises potassium hydroxide.
 5. The cell of claim 1 wherein the cathode further comprises graphitic carbon.
 6. The cell of claim 5 wherein the graphitic carbon comprises expanded graphite.
 7. The cell of claim 5 wherein the graphitic carbon comprises graphitic carbon nanofibers having a diameter less than 500 nanometers.
 8. The cell of claim 7 wherein said carbon nanofibers have a mean average diameter between about 50 and 300 nanometers.
 9. The cell of claim 8 wherein said carbon nanofibers have a mean average length between about 0.5 and 300 micron.
 10. The cell of claim 5 wherein the graphitic carbon comprises between 4 and 10 percent by weight of the cathode.
 11. The cell of claim 1 wherein the cathode comprises between about 82 and 90 percent by weight AgCuO₂.
 12. The cell of claim 1 wherein the cathode comprises between about 82 and 90 percent by weight Ag₂Cu₂O₃.
 13. The cell of claim 1 wherein the cathode active material is in particulate form having an average particle size between about 1 and 100 micron.
 14. The cell of claim 1 wherein said cell comprises less than 50 parts by weight mercury per million parts total cell weight.
 15. The cell of claim 7 wherein the graphitic carbon nanofibers comprise less than 200 parts by weight metal per million parts carbon.
 16. An electrochemical cell comprising an anode comprising anode active material, an aqueous alkaline electrolyte solution, a separator, and a cathode comprising AgCuo₂.
 17. The cell of claim 16 wherein said cell is nonrechargeable.
 18. The electrochemical cell of claim 16 wherein the anode active material comprises zinc.
 19. The cell of claim 16 wherein said AgCuO₂ comprises between about 3 and 15 percent by weight of said cathode.
 20. The cell of claim 16 wherein the electrolyte solution comprises potassium hydroxide.
 21. The cell of claim 16 wherein said cathode further comprises expanded graphite.
 22. The cell of claim 21 wherein said expanded graphite comprises between 4 and 10 percent by weight of said cathode.
 23. The cell of claim 16 wherein said cell comprises less than 50 parts by weight mercury per million parts total cell weight.
 24. An electrochemical cell comprising an anode comprising anode active material, an aqueous alkaline electrolyte solution, a separator, and a cathode comprising Ag₂Cu₂O₃.
 25. The cell of claim 24 wherein said cell is nonrechargeable.
 26. The electrochemical cell of claim 24 wherein the anode active material comprises zinc.
 27. The cell of claim 24 wherein said Ag₂Cu₂O₃ comprises between about 3 and 15 percent by weight of said cathode.
 28. The cell of claim 24 wherein the electrolyte solution comprises potassium hydroxide.
 29. The cell of claim 24 wherein said cathode further comprises expanded graphite.
 30. The cell of claim 29 wherein said expanded graphite comprises between 4 and 10 percent by weight of said cathode.
 31. The cell of claim 24 wherein said cell comprises less than 50 parts by weight mercury per million parts total cell weight. 